The present invention relates to a method and apparatus for adjusting the compression ratio of internal combustion engines, and more specifically to a method and apparatus for adjusting the position of the crankshaft with eccentric crankshaft main bearing supports.
Designs for engines having eccentric crankshaft main bearing supports have been known for sometime. In these engines the eccentric main bearings are rotated to adjust the position of the crankshaft""s axis of rotation. Poor rotational alignment of the eccentric main bearing supports is a problem for these engines because even small amounts of main bearing misalignment can cause rapid main bearing failure.
Significant forces bear down on the eccentric main bearing supports during operation of the engine. In modern passenger car engines main bearing loads can exceed 50 MPa. The forces exerted on the eccentric main bearing supports are at times significantly different from one eccentric main bearing support to the next. For example, in multi-cylinder engines a clockwise torque may be applied on a first eccentric main bearing support from the combustion pressure bearing down on the first piston, connecting rod and crank throw, and a counterclockwise torque may be applied on a second or third eccentric main bearing support from the inertial forces of the second piston and connecting rod pulling up on the second crank throw. As a second example, in a single cylinder engine having two eccentric main bearing supports the torque applied to the crank throw and the resistive torque at the power take off end of the crankshaft cause uneven loading on the eccentric main bearing supports. These large unequal forces are a problem because they cause the eccentric sections to rotate out of alignment with one another causing rapid failure of the crankshaft main bearings.
In U.S. Pat. No. 887,633, and in German patent DE 3644721 A1 a pinned linkage is show for adjusting the rotational alignment of the eccentric main bearing sections. U.S. Pat. No. 4,738,230 shows dowels extending from each eccentric main bearing support that are fitted into slots located in a slidable bar for adjusting the rotational alignment of the eccentric main bearing supports. U.S. Pat. Nos. 5,572,959 and 5,605,120 show gear teeth extending from eccentric main bearing supports that engage a layshaft with mating gears for adjusting the rotational alignment of the eccentric main bearing supports. U.S. Pat. No. 1,160,940 shows a bail shaped frame that connects adjacent eccentric sections for adjusting the rotational alignment of the eccentric sections. Poor alignment of the main bearings is a significant problem for each of these systems. In addition to poor main bearing alignment a number of these systems are not mechanically functional for other reasons, are impractical for mass production manufacture and assembly, and/or are not functional for engines having more than two main bearings. For example, U.S. Pat. No. 1,160,940 shows a bail shaped frame that is weakly connected to the eccentrics and that does not have a rigid construction. In addition to not rigidly hold the bearings in alignment. the system is not mechanically functional because the connecting rod does not clear the bail shaped frame. The system is also not functional for engines having more than two main bearings because it is not possible to slide the eccentric main bearing support onto the center crankshaft journal or journals.
A further problem with engines having rotatable eccentric main bearing supports in a fixed engine housing is that the location of the crankshaft rotational axis changes with change of compression ratio, making use of a conventional in-line clutch impossible. Geared power take-off couplings for engines having an adjustable crankshaft rotational axis are shown in the prior art, however a problem with these systems is that heavy structural reinforcing is required to rigidly hold the gear set in alignment. In addition to the problem of added weight, engine housing length is also increased.
German patent DE 3644721 A1 shows a gear set mounted to the free end of one of the eccentric crankshaft main bearing supports. The gear set has an intermediary shaft and an output shaft. The output shaft points generally away from the crankshaft, and has a fixed axis of rotation for all compression ration settings. A problem with the system shown in German patent DE 3644721 A1 is that during periods of high engine torque the end eccentric main bearing support may bend out of alignment, resulting in damage to the crankshaft main bearing. The gear set is also bulky and increases cranktrain friction losses due to the increased number of bearings and gear friction. U.S. Pat. No. 4,738.230 shows a first spur gear mounted on the crankshaft and a second spur gear having an axis of rotation that is concentric with the axis of rotation of the main bearing supports. These gears are too small to carry the torsional loads of the engine. U.S. Pat. No. 4,738,230 also shows a power take-off system having an internal or annular gear set. Heavy and lengthy structural reinforcing is required for holding the ring gear shaft in rigid alignment with the gear mounted on the end of the crankshaft. U.S. Pat. Nos. 5,443,043, 5,572,959 and 5,605,120 show a crankshaft having a fixed axis of rotation and an upper engine that changes position relative to its supporting frame when the compression ratio is changed. While a conventional in-line clutch can be employed with this arrangement, the position of the upper engine is changed when the compression ratio is changed, and the inertial mass of the upper engine prevents rapid adjustment of compression ratio.
In the present invention, a rotatable rigid crankshaft cradle is employed for holding the crankshaft main bearings in alignment. The crankshaft cradle is rotatably mounted in the engine on a pivot axis, and the crankshaft is mounted in the crankshaft cradle on a second axis off-set from the pivot axis. An actuator rotates the crankshaft cradle and adjusts the position of the crankshaft axis of rotation and the compression ratio of the engine. The crankshaft cradle rigidly holds the main bearings in precise alignment at all times and provides long bearing life. The crankshaft cradle provides rigid support of crankshafts for single and multi-cylinder engines, ranging from crankshafts having two main bearings for single and two cylinder engines, to crankshafts having five or more main bearings for in-line-four cylinder engines, V8 engines, as well as other engines. In addition to providing a long main bearing life, the variable compression ratio mechanism of the present invention is reliable and has a low cost.
Referring now to FIGS. 3, 4 and 5, in the preferred embodiment of the present invention a crankshaft cradle 60 is rotatably mounted in the engine housing on a pivot axis E, and a crankshaft 61 is mounted in the crankshaft cradle on a second axis A off-set from the pivot axis. The cradle includes two or more main bearing supports or eccentric members 62 and structural webbing 64 for rigidly holding the eccentric members and main bearings in alignment. One or more bearing caps 68 are fastened to the cradle with bolts or another type of fastener for securing the crankshaft in the cradle. The bearing caps are removable from the cradle permitting assembly of the crankshaft in the cradle. Operation of the main bearings without failure requires precise alignment of the main bearing supports at all times. According to the present invention, adjacent main bearing supports are held in rigid alignment at all times by structural webbing 64. More specifically. the structural webbing holds the main bearing supports in rigid alignment at all times providing a long service life for the main bearings.
FIG. 9 shows a second embodiment of the present invention. As shown in FIG. 9, crankshaft cradle 146 includes a first eccentric member, or main bearing support 160 and a second eccentric member, or main bearing support 162. The crankshaft cradle is assembled by sliding main bearing support 160 over a first end of crankshaft 152, and sliding the second main bearing support 162 over the second end of crankshaft 152 and rigidly fastening the main bearing supports together with one or more bolts 164. The main bearing supports include structural webbing for rigid attachment of the first main bearing support to the second main bearing support. The crankshaft applies large loads on main bearings 12, and the assembled crankshaft cradle 146 holds main bearings 12 in precise alignment under the high load conditions and more generally crankshaft cradle 146 holds main bearings 12 in precise alignment at all times.
An actuator first adjusts the rotational position of the crankshaft cradle about its pivot axis, and then locks the rotational position of the cradle in place. The actuator applies force on the cradle at a central location between the main bearings, and more generally between the front and back eccentric members, whereby twisting of the crankshaft cradle and miss alignment of the main bearings is minimized. Accordingly, the eccentric members are rigidly maintained in alignment providing a long main bearing life. Another advantage of the present invention is that the cradle has a small inertial mass, and the actuator can adjust compression ratio settings rapidly.
Power is transferred from the crankshaft to the power take-off shaft through gears 14 and 18. According to the present invention, gears 14 and 18 have a variable centerline distance and a variable backlash value. According to the present invention, the power take-off shaft is positioned to provide a small maximum gear backlash value for a large change in compression ratio. The power take-off coupling of the present invention provides long gear life exceptional reliability, low noise levels, and a low cost.
According to the present invention, the power takeoff shaft is located within xc2x145xc2x0 of an imaginary first plane and preferably within xc2x133xc2x0. The first plane passes through the crankshaft cradle pivot axis E and is perpendicular to the translation axis or centerline axis of the piston(s), providing a small change in backlash from one compression ratio setting to the next. More specifically, location of the power shaft within xc2x145xc2x0 of the first plane, and preferably within +33xc2x0, provides a small gear backlash, low gear noise, and long gear life. Additionally, gears 14 and 18 are mounted on parallel shafts and preferably have helical involute teeth permitting operation of the gears with small variations in centerline distance. Gears 14 and 18 are of automotive quality and have a diameter and width that provides a long gear life.
Prolonged operation of gears 14 and 18 without failure requires maintenance of parallel alignment of gear 14 and gear 18. According to the present invention, the crankshaft cradle holds the bearing elements the crankshaft, and gear 14 in precise parallel alignment at all times with the power take-off shaft and gear 18. According to the present invention, high structural loads are applied by the crankshaft on the bearing elements, and the crankshaft cradle rigidly holds the main bearing supports in precise parallel alignment at all times preventing failure of the bearing elements and preventing failure of gears 16 and 18.
The power take-off shaft is located adjacent to crankshaft cradle in the engine housing, and is rigidly supported with only a minimal increase of engine size and weight. A further advantage of the present invention is that the power take-off shaft may also serves as a balance shaft. FIG. 9 shows an embodiment of the present invention where the power take-off shaft also serves as a balance shaft for the engine. The engine shown in FIG. 9 has a small size and low bearing and gear friction in part because balancing and power take-off is accomplished with a single shaft.
Referring now to FIGS. 3, 4, 5 and 9, gear 14 mounted on the crankshaft transfers power from the crankshaft to a second gear 18 mounted on the power take-off shaft mounted in the engine housing. The crankshaft rotates on axis A and the power take-off shaft rotates on axis P Axis A and axis P are separated by a centerline distance. According to the present invention, rotation of the crankshaft cradle on the pivot axis E adjusts the position of the crankshaft, adjusts the compression ratio of the engine, and changes the centerline distance between axis A and axis P, causing the backlash clearance between gear 14 and gear 18 to change. According to the present invention, a small maximum gear backlash value is provided by locating the axis of rotation of gear 18 on or near a plane that passes through the axis of rotation of the crankshaft and that is generally perpendicular to the line of translation or centerline of the first piston(s).
The power take-off arrangement according to the present invention is significantly smaller, lighter, and less costly than prior art systems for engines having eccentric main bearing supports. Additionally, the present invention provides a low friction, compact, and light weight combined balance shaft and power takeoff gear set. The variable compression ratio mechanism according to the present invention holds the crankshaft main bearings in rigid alignment and provides a long bearing life. More specifically, the rigidity of the crankshaft cradle holds the bearings in alignment and prevents damage caused by bearing misalignment and vibration. The present invention is reliable and durable. The present invention can be manufactured using standard materials and mass-production methods, and has a low cost. Another advantage of the present invention is that the main bearings can be line bored, according to current manufacturing practices, to establish precise main bearing alignment. The variable compression ratio mechanism has a small inertial mass and a fast response providing rapid change of compression ratio.